Conventionally known work vehicles include a tractor for farm work and a wheel loader for construction work. Some of such work vehicles use a working machine attached thereto, corresponding to the work to be performed. Some working machines can be interlocked with the work vehicles. For example, the tractor can be interlocked with a loader, a sprayer, a broadcaster, and the like (refer to Patent Literature 1).
Generally, a working machine is provided with an interlock switch with which interlocking with the tractor is turned ON and OFF, and a display lamp indicating the interlocking with the tractor. Thus, the interlocking state with respect to the tractor is operated and displayed.